WASHINGTON — Republican Mitt Romney dug in Wednesday on his charge that President Barack Obama’s campaign is driven by “division and attack and hatred,” criticism aimed at cutting into Obama’s likeability and personal appeal with voters.

In some of his harshest words yet against the president, Romney said, “The president’s campaign is all about division and attack and hatred. I think he’ll do anything in his power to try and get re-elected.”

Romney’s comments escalated an already acrimonious campaign fueled by negative and sometimes false advertisements, as well as personal insults from the candidates and their surrogates.

Obama’s campaign said Romney’s fresh assertions seemed “unhinged.”

The president, campaigning Wednesday in Iowa, did not respond directly to Romney’s criticism. But first lady Michelle Obama, who joined the president on the final leg of his three-day bus trip through the Midwestern battleground, offered a vigorous defense of her husband’s character as she introduced him to the crowd.

“It all boils down to who you are and what you stand for,” Mrs. Obama said. “We all know who my husband is, don’t we? And we all know what he stands for.”

The president sought to refocus the day’s debate on GOP vice presidential candidate Paul Ryan’s proposed Medicare overhaul, which Democrats say could give them an opening with senior citizen voters. Romney and Ryan have been aggressive in going after Obama on that issue, saying he raided more than $700 billion from the Medicare trust fund to help pay for his health care overhaul.

Obama said Romney and Ryan’s criticism was “dishonest.”

“They are just throwing everything at the wall to see if this sticks,” Obama said. “I have strengthened Medicare.”

The latest rhetorical scuffle between the campaigns erupted Tuesday after Vice President Joe Biden told a largely black audience in Danville, Va., that Republicans would seek to “unchain Wall Street” and “put y’all back in chains” by loosening Wall Street regulations.

Biden later said he had meant to use the term “unshackled.” But he did not apologize, and he mocked the Romney campaign for showing outrage.

In his interview Wednesday on “CBS This Morning,” Romney said: “I can’t speak for anybody else, but I can say that I think the comments of the vice president were one more example of a divisive effort to keep from talking about the issues.”

Biden did not repeat the attention-grabbing line Wednesday during a campaign event in Blacksburg, Va.

Romney’s onslaught comes as polls show Obama with a narrow lead less than three months before the Nov. 6 election. On Saturday, Romney named Wisconsin Rep. Paul Ryan as his running mate, a pick aimed at energizing his party’s conservative base.

Now Romney, straying from his campaign’s efforts to stay singularly focused on jobs and the economy, is targeting Obama’s greatest strength — his likeability.

Every major poll in the past two months has found Obama’s favorability rating in positive territory, while Romney’s languishes at about even or worse and has deteriorated in some recent surveys.

Obama’s Iowa bus tour was aimed in part at maintaining his likeability in the midst of the bruising campaign. He made a trip to the Iowa State Fair, joined locals at a bar for a beer and dropped by a high school to wish teachers good luck in the new school year. The first lady’s presence on Wednesday, and her warm and teasing rapport with her husband, also aided in the effort.

Some of Romney’s efforts to chip away at Obama’s likeability have focused on negative ads run by the president’s campaign and a super political action committee supporting him. Priorities USA Action ran a commercial suggesting Romney was personally responsible for the death from cancer of the wife of a man who worked at a steel plant that was bought and subsequently shut down by Romney’s venture capital firm, Bain Capital.

“If you look at the ads that have been described and the divisiveness based upon income, age, ethnicity and so forth, it’s designed to bring a sense of enmity and jealousy and anger,” Romney said Wednesday.

The Romney campaign has run its own negative ads, including one widely discredited by independent fact-checkers that accuses Obama of gutting welfare reform. Romney’s team is also running an ad that criticizes Obama for raiding the Medicare trust fund, a charge the president’s team labeled dishonest and hypocritical.

Before Romney unleashed his striking criticism of the president’s campaign, much of the White House race this week had focused on Ryan’s austere budget proposals.

In states with large military and veteran populations — Florida, Ohio and Virginia among them — the Obama campaign plans to attack Ryan’s proposed cuts for veterans’ benefits and care, a campaign official said. The official was not authorized to discuss the campaign strategy publicly and requested anonymity.

In Colorado, Ohio and Iowa, the campaign sees opportunities to capitalize on Ryan’s proposed cuts to clean energy industries that are taking hold in those states. The Obama team will argue that cutting those investments would essentially cede new energy technologies — and the jobs that could come with them — to countries like China, the official said.

In Nevada and several other states, the campaign plans to push the impact of Ryan’s budget on education, citing estimates that it would cut 200,000 children a year from Head Start, an early education program, and reduce Pell grants for 10 million college students.

The campaign launched an ad Tuesday in five states — Colorado, Iowa, Nevada, Ohio and Virginia — that links Romney directly to the Ryan budget’s impact on college grants.

Obama’s team may launch other paid advertising on elements of Ryan’s budget soon. But for now, the campaign is focused on getting its message out in local media and directly to voters through its ample grass-roots network, which still trumps Romney’s ground game in some states.

Despite ramping up new areas of attack, Obama’s campaign is still eager to link Romney to Ryan’s Medicare proposals, both on the national level and in battleground states with a significant number of voters over the age of 65, including Florida, Ohio, Iowa and Pennsylvania.

The president’s pollsters wrote in a campaign memo that Ryan’s Medicare proposals are a “game changer” in Florida, the battleground state with the most electoral votes up for grabs in November.

Ryan didn’t say so, but the budgets he has written in the House both called for leaving in place the cuts to Medicare that he now criticizes. Romney has consistently favored restoring the funds, and his running mate said, “I joined the Romney ticket.”

The Obama campaign released a web video Wednesday that declares Romney and Ryan “plan to end Medicare as we know it.” It features news commentators and liberal analysts such as economist Paul Krugman declaring that Ryan’s House Republican budget would mean millions of older Americans would be unable to afford health care.

The video declares that Romney has lied about Obama’s record on Medicare, and says Obama’s proposal cuts payments to Medicare providers but offers more benefits to Medicare participants.

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